Self-opacifying enamel frits for the enamelling of aluminum or aluminum alloys

ABSTRACT

The present invention relates to self-opacifying enamel frit compositions that can be used for the enamelling of aluminium or aluminium alloys.

FIELD OF THE INVENTION

The present invention relates to self-opacifying enamel fritscompositions that can be used for the enamelling of aluminum or aluminumalloys.

BACKGROUND AND PRIOR ART

Many enamel frit compositions that can be used for the enamelling ofobjects of aluminum are known from the literature (e.g. U.S. Pat. No.2,467,114, DE 2 244 067, DE 2 119 777, U.S. Pat. No. 2,925,351, CA 85:36671p, CA 95: 174228g). Highly opaque, self-opacifying and chemicallyresistant enamelling cannot, however, be produced with these knownenamel frits. For this reason, use has hitherto been made of theadditional admixture of titanium dioxide, for example, as opacifier tothe so-called mill batch in order so to obtain opaque, chemicallyresistant enamelling on aluminum. This mill addition (up to 20 wt.%) inthe form of, for example, titanium dioxide leads to the titanium dioxidedispersing finely in the enamelling and, as a result of the highscattering power of the titanium dioxide, to the enamel layer maskingthe metal base.

In contrast to enamel frits for the enamelling of aluminum,self-opacifying enamel frits based on titanium dioxide for steel havealready existed for a relatively long time, but they cannot be appliedto aluminum, since they crystallize at temperatures of 590° C. to 650°C.

SUMMARY OF THE INVENTION

It was the object of the present invention to make available enamelfrits for aluminum or aluminum alloys, with which it is possible toproduce self-opacifying, chemically resistant enamelling on aluminumwithout additional mill additions in the form of opacifiers beingnecessary during the preparation of the mill batch (slick).

This object was achieved with enamel frits of a quite specialcomposition.

The invention provides self-opacifying, chemically resistant enamel fritcompositions for the enamelling of aluminum or aluminum alloys with athermal expansion coefficient of 460 to 475·10⁻⁷ K⁻¹ and a glasstransition temperature of 410° to 440° C., which are characterized inthat they have substantially the following composition:

    ______________________________________                                        32 to 37 wt. %         SiO.sub.2                                              0 to 4 wt. %           B.sub.2 O.sub.3                                        0 to 3 wt. %           Al.sub.2 O.sub.3                                       4 to 9 wt. %           Li.sub.2 O                                             10 to 18.5 wt. %       Na.sub.2 O                                             9 to 14 wt. %          K.sub.2 O                                              0 to 2 wt. %           MgO                                                    0 to 2 wt. %           SrO                                                    0 to 4 wt. %           BaO                                                    6 to 11 wt. %          V.sub.2 O.sub.5                                        0 to 3 wt. %           P.sub.2 O.sub.5                                        0 to 5 wt. %           Sb.sub.2 O.sub.3                                       14 to 21 wt. %         TiO.sub.2                                              0 to 2 wt. %           ZnO                                                    0 to 2 wt. %           SnO.sub.2                                              0 to 1 wt. %           MoO.sub.3                                              ______________________________________                                    

wherein the ratio of [TiO₂ +Sb₂ O₃ +SnO₂ +ZnO+Al₂ O₃ ] to [Li₂ O+Na₂O+K₂ O] amounts to 0.52 to 0.82.

DESCRIPTION OF PREFERRED EMBODIMENTS

The enamel frits preferably have the following composition:

    ______________________________________                                        32.5 to 36.4 wt. %     SiO.sub.2                                              0 to 3.2 wt. %         B.sub.2 O.sub.3                                        0.1 to 2.4 wt. %       Al.sub.2 O.sub.3                                       4 to 8.5 wt. %         Li.sub.2 O                                             10 to 18.5 wt. %       Na.sub.2 O                                             9 to 14 wt. %          K.sub.2 O                                              0 to 1 wt. %           MgO                                                    0 to 1 wt. %           SrO                                                    0 to 2.5 wt. %         BaO                                                    7 to 10.4 wt. %        V.sub.2 O.sub.5                                        1.8 to 2.9 wt. %       P.sub.2 O.sub.5                                        0 to 4.1 wt. %         Sb.sub.2 O.sub.3                                       14.2 to 20.4 wt. %     TiO.sub.2                                              0 to 1.8 wt. %         ZnO                                                    0 to 2 wt. %           SnO.sub.2                                              0 to 0.1 wt. %         MoO.sub.3                                              ______________________________________                                    

wherein the ratio of [TiO₂ +Sb₂ O+SnO₂ +ZnO+Al₂ O₃ ] to [Li₂ O+Na₂ O+K₂O] amounts to 0.52 to 0.82.

The enamel flits especially have the following composition:

    ______________________________________                                        32.5 to 36.4 wt. %     SiO.sub.2                                              0 to 2.2 wt. %         B.sub.2 O.sub.3                                        0.1 to 0.4 wt. %       Al.sub.2 O.sub.3                                       5.5 to 7.5 wt. %       Li.sub.2 O                                             12 to 17.5 wt. %       Na.sub.2 O                                             10 to 13 wt. %         K.sub.2 O                                              0 to 2.5 wt. %         BaO                                                    7 to 10.4 wt. %        V.sub.2 O.sub.5                                        1.8 to 2.3 wt. %       P.sub.2 O.sub.5                                        0 to 4.1 wt. %         Sb.sub.2 O.sub.3                                       16.3 to 20.4 wt. %     TiO.sub.2                                              0 to 0.9 wt. %         ZnO                                                    0 to 1.9 wt. %         SnO.sub.2                                              0 to 0.5 wt. %         MoO.sub.3                                              ______________________________________                                    

wherein the ratio of [TiO₂ +SnO₂ +Sb₂ O₃ +ZnO+Al₂ O₃ ] to [Li₂ O+Na₂O+K₂ O_(]) amounts to 0.56 to 0.82.

With the enamel frit compositions according to the invention, after theenamelling on aluminum a highly opaque, self-opacifying, white,chemically resistant enamel layer is obtained. This opaque enamel layercan be obtained without opacifiers having to be used in addition in themill batch.

With the special enamel frit composition a recrystallization of a partof the TiO₂ present in the frit can be achieved even at low temperatures(520° to 570° C.), so that an opaque white enamel layer can be producedduring the enamelling at firing temperatures of 520° to 570° C.

Through the use of the enamel frit compositions according to theinvention it is no longer necessary to admix opacifiers in addition tothe mill batch. The mill batch is thereby better handleable and nolonger as unstable as previously.

The enamel flits according to the invention can be applied for exampleby wet application to aluminium in the form of the so-called mill batchtogether with other mill additions to the aluminum substrate. Preferably100 parts by weight of the enamel frit according to the invention, 2 to10 parts by weight of auxiliary substances, 0 to 15 parts by weight ofadditional opacifiers, 0 to 15 parts by weight of pigments and 50 to 65parts by weight of water are used in the mill batch.

After application of the mill batch to the aluminum subtrate the latteris fired at temperatures between 520° and 570° C. A self-opacifyingenamel layer is obtained that has a high hiding (covering) power and ahigh chemical stability.

The enamelling produced with the enamel frits according to the inventionhas a high acid resistance as well as a high hiding power. Furthermore,it shows no tendency, even after many days at very high temperatures, todiscoloration (in particular not to greying or yellowing). In addition,relatively thin enamel layers can be produced with the enamel flitsaccording to the invention without in doing so the acid resistance beinginfluenced adversely or the hiding power being no longer adequate. Therelatively thin enamel layers have the great advantage that cracking ordeformations or other surface defects do not occur or occur less afterenamelling and cooling.

The enamel frits according to the invention can be manufacturedaccording to the known processes. The starting materials for thecorresponding oxide components in the enamel frit composition are mixed,thereafter melted and then chilled in water. The oxides of the enamelfrit components or other compounds that change into the oxides duringthe melting process are used as starting compounds.

During wet application to an aluminum substrate the enamel fritsaccording to the invention are mixed with other components in theso-called mill batch and subsequently sprayed onto the substrate, or thesubstrate is dipped in the mill batch. Usually used as mill additionsare auxiliary substances (boric acid, potassium hydroxide, sodiumsilicate, silica gel and/or carboxymethylcellulose), optionallyadditional opacifiers (TiO₂, SnO₂, Sb₂ O₃, ZnO, ZrO₂, ZrSiO₄) andoptionally pigments. After optional drying, firing is normally carriedout at 520°-570° C. for 2 to 8 minutes.

The invention will be illustrated in more detail with the aid of thefollowing examples.

EXAMPLES Preparation of the Enamel Frits

The various enamel frits were prepared by mixing and melting of theappropriate starting materials in an electric melting furnace. After themelting process the particular glass melt was chilled in water. Themelting process was carded out in each case at 1100 to 1150 for 15 to 30minutes. The compositions of the molten frits can be taken from Tables 1and 2.

Preparation of the Mill Batches

100 parts by weight of the enamel frits prepared as above are mixed ineach case with 4 parts by weight boric acid, 1 part by weight sodiumsilicate and 50 parts by weight water. The mixture is ground until theparticles have reached such a size that no more than 2% remain on asieve of mesh size 38 μm. The mixture thus prepared are used for theenamelling of the aluminum substrates. In further experiments up to 15parts by weight of opacifiers in addition are mixed with the millbatches.

Preparation of the Enamelling

The mill batches prepared as above are applied to aluminum sheets insuch an amount that after the enamelling a layer with a thicknessbetween 50 and 100 microns, preferably between 60 and 80 microns, ispresent. After the application of the mill batches to the aluminumsheets the latter are dried and subsequently fired at temperaturesbetween 520° and 570° C. The firing process lasts for 2 to 8 minutes.

The enamel frits 1 to 27 according to the invention (Table 1) provideenamel layers with good chemical resistance and hiding power. Theself-opacifying effect of these enamel layers is good and is intensifiedby the additional opacifiers in the mill batch. A thickness of theenamel layer of 50 to 60 μm is sufficient. The frits A to P according tothe prior art (Table 2) provide enamel layers without hiding power. Onlywith the use of 15 parts by weight and more of opacifier in the millbatch and a thickness of the enamel layer of 80 μm and more is anenamelling with good hiding power obtained.

If the frits according to the invention (e.g. 1, 5, 11, 21 and 24) areapplied to aluminum according to the above directions but fired attemperatures between 480° C. and 500° C., the enamelling shows no oronly weak self-opacification.

The frits 1 to 27 according to the invention are applied to aluminumaccording to the above directions and fired. The resulting enamelledaluminum sheets are kept in a furnace for 20 days at 360° C. Aftercooling-down the discoloration is measured. The enamelling produced withthe frits 1 to 27 according to the invention shows no discoloration,while the enamelling produced with the frits A to P, not according tothe invention, has discolorations.

                                      TABLE 1                                     __________________________________________________________________________          1  2  3  4  5  6  7  8  9  10 11 12 13 14                               __________________________________________________________________________    SiO.sub.2                                                                           34,9                                                                             35,1                                                                             35,2                                                                             34,4                                                                             34,1                                                                             34,8                                                                             35,1                                                                             34,8                                                                             34,7                                                                             34,4                                                                             34,4                                                                             34,4                                                                             34,4                                                                             34,5                             B.sub.2 O.sub.3                                                                     1,3                                                                              1,3                                                                              1,3                                                                              1,3                                                                              1,9                                                                              1,3                                                                              0  0,7                                                                              0,6                                                                              1,3                                                                              1,3                                                                              1,3                                                                              1,3                                                                              1,3                              Al.sub.2 O.sub.3                                                                    2,4                                                                              1,4                                                                              0,4                                                                              2,3                                                                              0,1                                                                              0,4                                                                              0,1                                                                              0,1                                                                              0,4                                                                              0,4                                                                              0,4                                                                              0,4                                                                              0,4                                                                              0,1                              Na.sub.2 O                                                                          15,5                                                                             15,6                                                                             15,6                                                                             15,3                                                                             15,5                                                                             15,5                                                                             15,1                                                                             15,2                                                                             15,2                                                                             17,3                                                                             15,3                                                                             15,3                                                                             15,3                                                                             15,4                             K.sub.2 O                                                                           10,2                                                                             11 11 10,8                                                                             10,7                                                                             10,9                                                                             11 10,9                                                                             10,9                                                                             10,8                                                                             10,8                                                                             10,8                                                                             10,8                                                                             10,8                             Li.sub.2 O                                                                          6,8                                                                              6,8                                                                              6,8                                                                              6,7                                                                              6,7                                                                              6,8                                                                              6,9                                                                              6,8                                                                              6,7                                                                              4,7                                                                              6,7                                                                              6,7                                                                              6,7                                                                              6,7                              BaO   1,8                                                                              1,8                                                                              1,8                                                                              1,8                                                                              1,8                                                                              1,8                                                                              1,8                                                                              1,8                                                                              1,8                                                                              1,8                                                                              1,8                                                                              0  1,8                                                                              1,8                              Sb.sub.2 O.sub.3                                                                    2,3                                                                              2,3                                                                              0  2,2                                                                              2,2                                                                              2,3                                                                              2,2                                                                              2,2                                                                              2,3                                                                              2,2                                                                              2,2                                                                              2,2                                                                              2,2                                                                              2,2                              V.sub.2 O.sub.5                                                                     7,7                                                                              7,8                                                                              7,8                                                                              7,6                                                                              7,6                                                                              7,7                                                                              7,8                                                                              7,7                                                                              7,4                                                                              7,6                                                                              7,6                                                                              7,6                                                                              7,6                                                                              7                                P.sub.2 O.sub.5                                                                     2,3                                                                              2,3                                                                              2,3                                                                              2,3                                                                              2,3                                                                              2,3                                                                              2,4                                                                              2,3                                                                              2,6                                                                              2,3                                                                              2,3                                                                              2,3                                                                              1,8                                                                              2,9                              TiO.sub.2                                                                           14,2                                                                             14,6                                                                             17,6                                                                             15,3                                                                             17,1                                                                             14,2                                                                             17,6                                                                             17,4                                                                             17,4                                                                             17,2                                                                             17,2                                                                             17,2                                                                             17,2                                                                             17,3                             SnO.sub.2                                                                           0  0  0  0  0  0  0  0  0  0  0  0  0  0                                ZnO   0  0  0  0  0  0  0  0  0  0  0  1,8                                                                              0  0                                MgO   0  0  0  0  0  0  0  0  0  0  0  0  0,5                                                                              0                                Summe 100,1                                                                            100,0                                                                            99,8                                                                             100,0                                                                            100,0                                                                            100,0                                                                            100,0                                                                            99,9                                                                             100,0                                                                            100,0                                                                            100,0                                                                            100,0                                                                            100,0                                                                            100,0                            Li.sub.2 O/R.sub.2 O                                                                0,209                                                                            0,204                                                                            0,204                                                                            0,204                                                                            0,204                                                                            0,205                                                                            0,209                                                                            0,207                                                                            0,204                                                                            0,143                                                                            0,204                                                                            0,204                                                                            0,204                                                                            0,204                            X/R.sub.2 O                                                                         0,536                                                                            0,545                                                                            0,566                                                                            0,573                                                                            0,644                                                                            0,596                                                                            0,600                                                                            0,617                                                                            0,619                                                                            0,631                                                                            0,631                                                                            0,631                                                                            0,631                                                                            0,632                            __________________________________________________________________________          15 16  17 18 19  20 21 22 23 24 25  26 27                               __________________________________________________________________________    SiO.sub.2                                                                           33,7                                                                             34,2                                                                              34,1                                                                             33,9                                                                             34,5                                                                              34,4                                                                             33,7                                                                             34,4                                                                             33,8                                                                             33,1                                                                             33,1                                                                              32,9                                                                             32,5                             B.sub.2 O.sub.3                                                                     1,2                                                                              1,3 1,3                                                                              1,3                                                                              2,2 1,1                                                                              1,3                                                                              3,2                                                                              0  1,2                                                                              1,3 1,8                                                                              1,2                              Al.sub.2 O.sub.3                                                                    2,3                                                                              0,4 0,4                                                                              0,4                                                                              0,3 0,3                                                                              0,4                                                                              0,3                                                                              0,1                                                                              0,4                                                                              0,4 0,1                                                                              0,4                              Na.sub.2 O                                                                          15 15  14,8                                                                             14,5                                                                             13,1                                                                              12,9                                                                             15 12,4                                                                             14,5                                                                             14,7                                                                             12,8                                                                              14,9                                                                             14,4                             K.sub.2 O                                                                           10,6                                                                             10,8                                                                              10,9                                                                             10,9                                                                             12,7                                                                              12,6                                                                             10,6                                                                             12,6                                                                             10,6                                                                             10,4                                                                             10,4                                                                              10,3                                                                             10,2                             Li.sub.2 O                                                                          6,5                                                                              6,7 6,7                                                                              6,7                                                                              6,3 6,3                                                                              6,5                                                                              6,3                                                                              6,5                                                                              6,4                                                                              8,3 6,4                                                                              6,3                              BaO   1,7                                                                              1,8 1,8                                                                              1,8                                                                              0   0  1,8                                                                              0  1,7                                                                              1,7                                                                              1,7 1,7                                                                              1,7                              Sb.sub.2 O.sub.3                                                                    4,1                                                                              2,3 2,3                                                                              2,3                                                                              0   1,5                                                                              2,2                                                                              0  4,1                                                                              2,2                                                                              4   4  4                                V.sub.2 O.sub.5                                                                     7,5                                                                              7,7 7,7                                                                              7,7                                                                              9,9 9,9                                                                              7,5                                                                              9,8                                                                              7,6                                                                              7,4                                                                              7,4 7,4                                                                              7,2                              P.sub.2 O.sub.5                                                                     2,2                                                                              2,3 2,3                                                                              2,3                                                                              1,8 1,8                                                                              2,2                                                                              1,8                                                                              2,2                                                                              2,2                                                                              2,2 2,2                                                                              2,2                              TiO.sub.2                                                                           15 17,3                                                                              17,4                                                                             17,5                                                                             19,2                                                                              19,2                                                                             16,9                                                                             19,2                                                                             18,9                                                                             18,5                                                                             18,5                                                                              18,4                                                                             20                               SnO.sub.2                                                                           0  0   0  0  0   0  1,9                                                                              0  0  1,9                                                                              0   0  0                                ZnO   0  0   0  0  0   0  0  0  0  0  0   0  0                                MgO   0  0,4 0,8                                                                              1,2                                                                              0   0  0  0  0  0  0   0  0                                Summe 99,8                                                                             100,2                                                                             100,5                                                                            100,5                                                                            100,0                                                                             100,0                                                                            100,0                                                                            100,0                                                                            100,0                                                                            100,1                                                                            100,1                                                                             100,1                                                                            100,1                            Li.sub.2 O/R.sub.2 O                                                                0,202                                                                            0,206                                                                             0,207                                                                            0,209                                                                            0,196                                                                             0,198                                                                            0,202                                                                            0,201                                                                            0,206                                                                            0,203                                                                            0,263                                                                             0,203                                                                            0,204                            X/R.sub.2 O                                                                         0,632                                                                            0,643                                                                             0,648                                                                            0,648                                                                            0,657                                                                             0,667                                                                            0,686                                                                            0,695                                                                            0,716                                                                            0,728                                                                            0,756                                                                             0,756                                                                            0,816                            __________________________________________________________________________     X = Al.sub.2 O.sub.3 + Sb.sub.2 O.sub.3 + TiO.sub.2 + SnO.sub.2 + ZnO         R.sub.2 O = Na.sub.2 O + K.sub.2 O + Li.sub.2 O                               All data in wt. %                                                        

                                      TABLE 2                                     __________________________________________________________________________    A        B  C  D  E  F  G  H  I  J  K  L  M  N  O  P                          __________________________________________________________________________    SiO.sub.2                                                                           33,6                                                                             35,1                                                                             33,1                                                                             34,4                                                                             34,1                                                                             35,1                                                                             33,1                                                                             33,2                                                                             32,9                                                                             32,5                                                                             32,5                                                                             34,4                                                                             31,5                                                                             35,1                                                                             32,9                                                                             31,5                       B.sub.2 O.sub.3                                                                     1,1                                                                              1,3                                                                              1,3                                                                              1,3                                                                              1,3                                                                              1,3                                                                              1,2                                                                              2  0  1,2                                                                              1,2                                                                              1,3                                                                              0  1,3                                                                              0  0                          Al.sub.2 O.sub.3                                                                    0,6                                                                              0,4                                                                              0,4                                                                              0,4                                                                              3,8                                                                              0,4                                                                              0,4                                                                              0,1                                                                              1,1                                                                              0,4                                                                              2,2                                                                              0,4                                                                              0,1                                                                              0,4                                                                              1,1                                                                              0,1                        Na.sub.2 O                                                                          18 13,6                                                                             12,8                                                                             15,3                                                                             15,1                                                                             19,6                                                                             14,7                                                                             21,5                                                                             13,6                                                                             14,4                                                                             14,4                                                                             17,3                                                                             15,1                                                                             19,6                                                                             17,6                                                                             19,1                       K.sub.2 O                                                                           12 11 10,4                                                                             10,8                                                                             10,7                                                                             7  10,4                                                                             12,1                                                                             10 10,2                                                                             10,2                                                                             10,8                                                                             10,6                                                                             11 10 10,6                       Li.sub.2 O                                                                          2,5                                                                              8,8                                                                              8,3                                                                              6,7                                                                              6,6                                                                              6,8                                                                              6,4                                                                              1,8                                                                              7,8                                                                              6,3                                                                              6,3                                                                              4,7                                                                              5,4                                                                              2,8                                                                              3,8                                                                              1,4                        BaO   0  1,8                                                                              1,7                                                                              1,8                                                                              1,7                                                                              1,8                                                                              1,7                                                                              0  1,7                                                                              1,7                                                                              1,7                                                                              1,8                                                                              5,9                                                                              1,8                                                                              1,7                                                                              5,9                        Sb.sub.2 O.sub.3                                                                    0  2,3                                                                              4  0  2,2                                                                              2,3                                                                              0  0  0  2,1                                                                              2,1                                                                              2,2                                                                              0  2,3                                                                              0  0                          V.sub.2 O.sub.5                                                                     9,3                                                                              7,6                                                                              7,4                                                                              7,6                                                                              7,6                                                                              7,8                                                                              7,4                                                                              4,6                                                                              8  7,2                                                                              7,2                                                                              7,6                                                                              4  7,6                                                                              8  4                          P.sub.2 O.sub.5                                                                     2,2                                                                              2,3                                                                              2,2                                                                              2,3                                                                              2,2                                                                              2,3                                                                              2,2                                                                              2,3                                                                              1,6                                                                              2,2                                                                              2,2                                                                              2,3                                                                              0,1                                                                              2,3                                                                              1,6                                                                              0,1                        TiO.sub.2                                                                           20,7                                                                             15,6                                                                             18,5                                                                             15,3                                                                             15,1                                                                             15,6                                                                             18,5                                                                             22,4                                                                             23,3                                                                             20 20 17,2                                                                             21,1                                                                             15,6                                                                             23,3                                                                             21,1                       SnO.sub.2                                                                           0  0  0  4,2                                                                              0  0  4,1                                                                              0  0  1,9                                                                              0  0  5  0  0  5                          ZnO   0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0                          MgO   0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0                          MoO.sub.3                                                                           0  0  0  0  0  0  0  0  0  0  0  0  1  0  0  1                          Summe 100,0                                                                            99,8                                                                             100,1                                                                            100,1                                                                            99,9                                                                             100,0                                                                            100,1                                                                            100,0                                                                            100,0                                                                            100,1                                                                            100,0                                                                            100,0                                                                            99,8                                                                             99,80                                                                            100,0                                                                            99,8                       Li.sub.2 O/R.sub.2 O                                                                0,077                                                                            0,263                                                                            0,263                                                                            0,204                                                                            0,204                                                                            0,204                                                                            0,203                                                                            0,051                                                                            0,248                                                                            0,204                                                                            0,204                                                                            0,143                                                                            0,174                                                                            0,084                                                                            0,121                                                                            0,045                      X/R.sub.2 O                                                                         0,655                                                                            0,548                                                                            0,727                                                                            0,607                                                                            0,636                                                                            0,548                                                                            0,730                                                                            0,636                                                                            0,777                                                                            0,790                                                                            0,786                                                                            0,604                                                                            0,842                                                                            0,548                                                                            0,777                                                                            0,842                      __________________________________________________________________________     X = Al.sub.2 O.sub.3 + Sb.sub.2 O.sub.3 + TiO.sub.2 + SnO.sub.2 + ZnO         R.sub.2 O = Na.sub.2 O + K.sub.2 O + Li.sub.2 O                               All data in wt. %                                                        

We claim:
 1. A self-opacifying and chemically resistant enamel fritcomposition for the enamelling of aluminum or aluminum alloys with athermal expansion coefficient of 460 to 475·10-⁷ K-¹ and a glasstransition temperature of 410° to 440° C., consisting of:

    ______________________________________                                        32 to 37 wt. %         SiO.sub.2                                              0 to 4 wt. %           B.sub.2 O.sub.3                                        0 to 3 wt. %           Al.sub.2 O.sub.3                                       4 to 9 wt. %           Li.sub.2 O                                             10 to 18.5 wt. %       Na.sub.2 O                                             9 to 14 wt. %          K.sub.2 O                                              0 to 2 wt. %           MgO                                                    0 to 2 wt. %           SrO                                                    0 to 4 wt. %           BaO                                                    6 to 11 wt. %          V.sub.2 O.sub.5                                        0 to 3 wt. %           P.sub.2 O.sub.5                                        0 to 5 wt. %           Sb.sub.2 O.sub.3                                       14 to 21 wt. %         TiO.sub.2                                              0 to 2 wt. %           ZnO                                                    0 to 2 wt. %           SnO.sub.2                                              0 to 1 wt. %           MoO.sub.3                                              ______________________________________                                    

wherein the ratio of [TiO₂ +Sb₂ O₃ +SnO₂ +ZnO+Al₂ O₃ ] to [Li₂ O+Na₂O+K₂ O] amounts to 0.52 to 0.82.
 2. Slip for enamelling on aluminum oraluminum alloys, characterized in that the slip has the followingcomposition:100 parts by weight of an enamel frit having the followingcomposition:

    ______________________________________                                        32 to 37 wt. %         SiO.sub.2                                              0 to 4 wt. %           B.sub.2 O.sub.3                                        0 to 3 wt. %           Al.sub.2 O.sub.3                                       4 to 9 wt. %           Li.sub.2 O                                             10 to 18.5 wt. %       Na.sub.2 O                                             9 to 14 wt. %          K.sub.2 O                                              0 to 2 wt. %           MgO                                                    0 to 2 wt. %           SrO                                                    0 to 4 wt. %           BaO                                                    6 to 11 wt. %          V.sub.2 O.sub.5                                        0 to 3 wt. %           P.sub.2 O.sub.5                                        0 to 5 wt. %           Sb.sub.2 O.sub.3                                       14 to 21 wt. %         TiO.sub.2                                              0 to 2 wt. %           ZnO                                                    0 to 2 wt. %           SnO.sub.2                                              ______________________________________                                    

wherein the ratio of [TiO₂ +Sb₂ O₃ +SnO₂ +ZnO+Al₂ O₃ ] to [Li₂ O+Na₂O+K₂ O] amounts to 0.52 to 0.82;

    ______________________________________                                        0 to 15     parts by weight opacifier;                                        2 to 10     parts by weight auxiliary substances;                             0 to 15     parts by weight pigments; and                                     50 to 65    parts by weight water.                                            ______________________________________                                    


3. Enamel frit composition according to claim 1, characterized in thatthe frit has the following composition:

    ______________________________________                                        32.5 to 36.4 wt. %     SiO.sub.2                                              0 to 3.2 wt. %         B.sub.2 O.sub.3                                        0.1 to 2.4 wt. %       Al.sub.2 O.sub.3                                       4 to 8.5 wt. %         Li.sub.2 O                                             10 to 18.5 wt. %       Na.sub.2 O                                             9 to 14 wt. %          K.sub.2 O                                              0 to 1 wt. %           MgO                                                    0 to 1 wt. %           SrO                                                    0 to 2,5 wt. %         BaO                                                    7 to 10.4 wt. %        V.sub.2 O.sub.5                                        1.8 to 2.9 wt. %       P.sub.2 O.sub.5                                        0 to 4.1 wt. %         Sb.sub.2 O.sub.3                                       14.2 to 20.4 wt. %     TiO.sub.2                                              0 to 1.8 wt. %         ZnO                                                    0 to 2 wt. %           SnO.sub.2                                              0 to 0.1 wt. %         MoO.sub.3                                              ______________________________________                                    

wherein the ratio of [TiO₂ +Sb₂ O₃ +SnO₂ +ZnO +Al₂ O₃ ] to [Li₂ O+Na₂O+K₂ O] amounts to 0.53 to 0.82.
 4. Enamel frit compositions accordingto claim 1, characterized in that the frit has the followingcomposition:

    ______________________________________                                        32.5 to 36.4 wt. %     SiO.sub.2                                              0 to 2.2 wt. %         B.sub.2 O.sub.3                                        0.1 to 0.4 wt. %       Al.sub.2 O.sub.3                                       5.5 to 7.5 wt. %       Li.sub.2 O                                             12 to 17.5 wt. %       Na.sub.2 O                                             10 to 13 wt. %         K.sub.2 O                                              0 to 2.5 wt.%          BaO                                                    7 to 10.4 wt. %        V.sub.2 O.sub.5                                        1.8 to 2.3 wt. %       P.sub.2 O.sub.5                                        0 to 4.1 wt. %         Sb.sub.2 O.sub.3                                       16.3 to 20.4 wt. %     TiO.sub.2                                              0 to 0.9 wt. %         ZnO                                                    0 to 1.9 wt. %         SnO.sub.2                                              0 to 0.5 wt. %         MoO.sub.3                                              ______________________________________                                    

wherein the ratio of [TiO₂ +SnO₂ +Sb₂ O₃ +ZnO+Al₂ O₃ ] to [Li₂ O+Na₂O+K₂ O] amounts to 0.56 to 0.82.